[PATCH 6.6 30/84] sctp: avoid NULL dereference when chunk data buffer is missing

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

6.6-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Alexey Simakov <bigalex934@gmail.com>

[ Upstream commit 441f0647f7673e0e64d4910ef61a5fb8f16bfb82 ]

chunk->skb pointer is dereferenced in the if-block where it's supposed
to be NULL only.

chunk->skb can only be NULL if chunk->head_skb is not. Check for frag_list
instead and do it just before replacing chunk->skb. We're sure that
otherwise chunk->skb is non-NULL because of outer if() condition.

Fixes: 90017accff61 ("sctp: Add GSO support")
Signed-off-by: Alexey Simakov <bigalex934@gmail.com>
Acked-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Link: https://patch.msgid.link/20251021130034.6333-1-bigalex934@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 net/sctp/inqueue.c | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/net/sctp/inqueue.c b/net/sctp/inqueue.c
index 5c16521818058..f5a7d5a387555 100644
--- a/net/sctp/inqueue.c
+++ b/net/sctp/inqueue.c
@@ -169,13 +169,14 @@ struct sctp_chunk *sctp_inq_pop(struct sctp_inq *queue)
 				chunk->head_skb = chunk->skb;
 
 			/* skbs with "cover letter" */
-			if (chunk->head_skb && chunk->skb->data_len == chunk->skb->len)
+			if (chunk->head_skb && chunk->skb->data_len == chunk->skb->len) {
+				if (WARN_ON(!skb_shinfo(chunk->skb)->frag_list)) {
+					__SCTP_INC_STATS(dev_net(chunk->skb->dev),
+							 SCTP_MIB_IN_PKT_DISCARDS);
+					sctp_chunk_free(chunk);
+					goto next_chunk;
+				}
 				chunk->skb = skb_shinfo(chunk->skb)->frag_list;
-
-			if (WARN_ON(!chunk->skb)) {
-				__SCTP_INC_STATS(dev_net(chunk->skb->dev), SCTP_MIB_IN_PKT_DISCARDS);
-				sctp_chunk_free(chunk);
-				goto next_chunk;
 			}
 		}
 
-- 
2.51.0